This invention relates to an oven and more particularly, to a novel combination of microwave and gas oven for heat-treating foodstuff based on characteristics of high frequency heating through a source of microwave energy and heating by physical burning through a gas burner, with foodstuff being exposed in the atmosphere of said combined energy within an oven.
One of the difficulties in cooking encountered by using a conventional electronic oven, has been the inability of such microwave energy to scorch or brown surfaces of foodstuffs to such an extent as will stimulate appetite and, thus the oven of this type is mainly used for limited cooking purposes, such as reheating or defreezing of foodstuffs.
On the contrary to the heating characteristics of the electronic oven mentioned above, a gas oven is a handy cooking device especially for browning surfaces of foodstuffs due to its fundamental heating system while being not so effective for defreezing or reheating of foodstuffs, and thus, this type of cooking device is also available only for limited range of cooking as mentioned above. The combination microwave and gas oven has already been proposed, for example, by U.S. Pat. No. 3,789,178, wherein the combination microwave and gas oven is provided with a divider shelf preferably horizontally disposed, thereby dividing the oven cavity into a cooking section and a section containing the gas heating apparatus. The outer boundary of the shelf forms a low impedance choke directly coupled to the cooking section with a perimetrical shelf holder, thereby terminating microwave energy fed to the cooking section and preventing degradation of the gas heating apparatus provided therebelow.
The known combination microwave and gas oven as described above has such a disadvantage that energy supplying source for the oven portion such as a gas burner or the like must be still provided with relatively large capacity for quick heat-treatment of an object to be heated.
However, if the heat is excessively added to the combination of microwave and gas oven mentioned above, there appears a tendency to overheat the source of the microwave supplies such as a magnetron. Furthermore, even the combination of microwave and gas oven which can transmit heat under the forced convection condition therein, has not been applicable for browning surfaces of foodstuffs within relatively short period of cooking time due to its lack of the desired radiant heat.
Furthermore, when a fan is provided for circulating the heat generated by a heater such as the electric heater in the heating cavity of the oven mentioned above, there is a problem of leakage of microwave resulting from the construction of a shaft of the fan for circulation, wherein since the shaft connected with the fan located inside the heating cavity will pass through the boundary of the heating cavity and come out to be connected with the driving motor, a leakage of microwave cannot be avoided and naturally occurs in the vicinity of a through hole for setting said shaft.
Accordingly, an essential object of the present invention is to provide a combination microwave and gas oven which will combine both characteristics of a microwave oven and that of a gas oven, whereby disadvantages in each of the cooking method is compensated for each other, and which can treat foodstuffs in many ways as far as the range of browning, defreezing and reheating.
Another important object of the present invention is to provide a combination microwave and gas oven of the above described type, which is provided with a fan for effectively circulating the heat in a heating cavity, and also with a proper protectional member against over-heating of a source of microwave energy.
A further object of the present invention is to provide a combination microwave and gas oven of the above described type, wherein a choking system is provided for terminating leakage of microwave energy especially with respect to a shaft of a circulation fan and its connectors.
A still further object of the present invention is to provide a combination microwave and gas oven of the above described type, which is simple in construction and efficient in operation, and can be manufactured at low cost.